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Eco-environmental Changes and Causal Analysis in the Source Regions of the Yellow River

WANG Gen-xu, SHEN Yong-ping, CHENG Guo-dong (State Key Laboratory of Frozen Soil Engineering, CAREERI, CAS, Lanzhou Gansu 730000. China) (Resource and Environment College of Lanzhou University: Lanzhou Gansu 730000. China)  
Based on three phases of satellite image data and field investigation, the eco-environmental evolution processes since the 1970s were analyzed. Analyses and discussions were made in this paper aimed at the understanding of the trend and causes of eco- environment changes in the regions over the last 20 a. The causes responsible for the environmental changes in the regions were explored in accordance with climate change and human activity. It is found that the eco-environment in the source regions of the Yellow River markedly degraded during the period of the 1980s-1990s compared with the 1970s. Especially from the mid-1990s, high-cold grassland and high-cold meadow vegetations seriously degraded, together with rapid desertification. The area of vegetation degradation increased from 24.5% in the 1980s to 34.5% of the total area of grassland and high-cold meadow in the 1990s. The expanding rate of desertification increased from 3.96% in the 1980s to 34.72% in the 1990s. Climate in the regions is becoming dry and warm, and permafrost is gradually degrading. Air temperature in the source regions of the Yellow River has been rising since 1954. Permafrost environment of the regions altered markedly, with an expansion of thawed.area and an increase in seasona thawing depth. Degradation of Permafrost led to a decrease of soil moisture content in root zone and surface soil desertification. In spite of this, summer precipitation in the regions also showed a decreasing tendency. Such regional climate change is not favorable for the normal growth of vegetation and thus will be causing extensive vegetation degradation. At the statuse of present the seasonal distribution of rangelands is unbalanced and irrational use. Consequently, cold-season rangelands are seriously overgrazed and thus causing pasture degradation. In addition, rodent and insect damages in the headwaiers are serious, covering 6% - 21 % of the total rangeland area.
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